1. Field of the Invention
This invention relates to optical information recording media which are able to record and reproduce optical information at high speed and high density by application of optical energy. The invention also relates to a method for efficiently making such recording media.
2. Description of the Prior Art
Systems of recording and reproducing high density information by utilization of a laser beam are well known. Typical recording media used for these recording and reproducing systems are those media which have a substrate and a thin film made predominantly of Te or TeOx.sub.1 (0&lt;x.sub.1 &lt;2), which is a mixture of Te and TeO.sub.2, and formed on the substrate. These media are described, for example, in Japanese Laid-open Pat. Application Nos. 50-46317, 50-46318, 50-46319 and U.S. Pat. No. 3971874. Aside from the main constituent, PbOx.sub.5 (0&lt;x.sub.5 &lt;1), SbOx.sub.6 (0&lt;x.sub.6 &lt;1.5), VOx.sub.7 (0&lt;x.sub.7 &lt;2.5) and the like are added as additives. These recording media have a greatly varying transmission upon irradiation of an optical beam.
The recent trend toward the compactness and simplicity of a recording and reproducing apparatus places a limitation on the output power of a laser beam source. For the recording and reproducing operations using a small-sized He-Ne laser oscillator or a semiconductor laser oscillator having an output power within 20 mW, the known recording media using TeOx (0&lt;x&lt;2) are not satisfactory because of the insufficient sensitivity thereof. Alternatively, where recorded information is reproduced as a variation in quantity of reflected light, such a variation as to be high enough for the reproduction cannot be obtained.
In order to overcome the above drawbacks, attempts were made in which an additive having a low melting point was added to TeOx (0&lt;x&lt;2) so that the threshold temperature lowered. For instance, TlOx (0&lt;x&lt;1.5) having a melting point of 300.degree. C. for Tl.sub.2 O was added. However, the addition of this type of additive was not necessarily satisfactory.
On the other hand, in order to produce a larger variation of optical characteristics accompanied by the phase change of the oxide, attempts have been made in which a refractive index of a medium was increased. For these purposes, additives having a large ionic polarizability and a high density are used, e.g. BiOx.sub.2 and InOx.sub.2 (0&lt;x.sub.2 &lt;1.5). These media are described, for example, in Japanese Pat. Application Nos. 53-109002 and 54-71506.
According to the above methods, the recording medium based on the TeOx compound could be used for recording by a semiconductor laser and for reproduction according to variations in amount of reflected light.
However, as the information-oriented society is being advanced, a higher speed of information transmission is required. This necessitates a higher recording speed, higher reproduction speed and higher recording sensitivity than is now experienced in this art.